Did The Viking Squirrel Trade Spread Leprosy?

Did the Viking trade in red squirrels spread leprosy in Medieval Europe? A new study raises many questions but provides few solid answers.

A red squirrel sits in the snow in Wiesbaden, Germany, on March 12, 2013. Winter came back to wide parts of the country, bringing snow and cold temperatures. (Photo credit: FREDRIK VON ERICHSEN/AFP/Getty Images)

A research project launched in England in 2016 aimed to better understand how leprosy affected British red squirrels. The disease was first found in red squirrels living within Scotland. Red squirrels with leprosy often develop lesions on their ears, appendages and even their muzzles. This has allowed the grey squirrel population to rise significantly on the island, since it appears grey squirrels do not contract leprosy.

But how did leprosy get to England in the first place? A new article in the Journal of Medical Microbiology suggests that leprosy-infected red squirrels go back a number of centuries, at least to pre-Norman England (5th-11th c. CE). This find is based in part on a skull of a woman found in a garden in Hoxne, Suffolk, between 1960 and 1990. The skull exhibited the characteristics of lepromatous leprosy (LL). Recent radiocarbon dating of the skull suggests the woman lived between 885 and 1015 CE.

A woman feeds a leper in bed in this late 13th c. Swiss manuscript now at the J. Paul Getty Museum (Ms. Ludwig VIII 3, fol. 43).Getty Open Content Program

As Cambridge archaeologist Sarah Inskip and the rest of the authors of the study noted, ancient DNA analysis was also performed on the skull: "aDNA confirmed the presence of mycobacterium leprae and genotyping demonstrated an ancestral variant of subtype 3I, the same lineage recently identified in living squirrels in the south of England." There were in fact multiple strains of leprosy in early Medieval England: "at least two distinct strains of leprosy existed in Medieval England. Type 3 strains were present from the fifth– sixth century, while strains from the second branch (type 2F strains) are known from the eleventh century."

In medieval skeletons recovered from Winchester, UK showed only the M. leprae species. However, a pivotal study published by Charlotte Avanzi et al. in 2016 discovered that separate red squirrel populations have M. lepromatosis and M. leprae. As such, the archaeologists have suggested that it is an "attractive theory" that medieval red squirrels passed leprosy onto humans, just as armadillos can today.

It is hypothesized by the authors that red squirrels carrying leprosy perhaps came to inhabit England after first being imported to East Anglia by traders from Scandinavia and the area of the Baltic Sea. There was an active trade in squirrel meat, fur and--they allege--squirrels were sometimes kept as pets.

As science writer Nancy Marie Brown explores in her book, Ivory Vikings, medieval writers confirm that there was a cycle of trade between Scandinavia, the Baltic regions and England that introduced a number of products to the island, including squirrel pelts: "According to Ibn Rusta of Isfahan, who wrote a seven-volume encyclopedia between 903 and 913, the Rus 'earn their living by trading in sable, grey squirrel, and other furs. They sell them for silver coins..." Similarly, the Vikings also traded sable, fox, beaver, and squirrels.

Footwear from the Viking era at the Lofotr Viking Museum includes fur-lined shoes. Use of squirrel fur was common among Vikings and the Rus,Justin Hall (CC-BY-2.0)

Whether the Viking squirrel trade was truly responsible for bringing leprosy to humans living in England is far from certain and hinges on a number of factors. Medieval medical historian Monica H. Green, a professor at Arizona State University, has raised serious issues with the current study. As she points out, "No genetics data confirms that [the] woman in Hoxne was infected by squirrels, nor has zoonotic transmission from squirrels been documented in any other case. But, they are absolutely right that UK squirrels have been shown to carry same strain as one documented in humans in medieval England & in modern N[orth] America."

A second problem lies in our understanding of the squirrel trade itself. In order to substantiate the squirrel fur trade, the authors of the leprosy study cited a well known history of England's fur trade from 1966, written by Elspeth M. Veale. The study notes that it is doubtful that furs can themselves transmit leprosy. Consequently, the question hinges in part on whether medieval people in England actually kept red squirrels as pets.

As Green remarks, use of the Veale book provides a historical context without supporting the claim of squirrel pets: "They suggest that people kept squirrels as pets, but cite no source for this assertion. In short, then, an interesting speculation has been proposed. Clinching it with evidence will be the task of other research. There is, in fact, a bigger puzzle out there having to do w[ith] a new species of leprosy discovered by X.-Y. Han in 2008, Mycobacterium lepromatosis. This has also been found in UK squirrels."

There also remains the need for further study of leprosy transmission between animals and humans. Green underscores that this is imperative to understanding the spread of the disease in the past and today: "we need to explore whether squirrels (or some related species) are the long-term hosts of the disease, who periodically transmit it to humans, or whether humans give it to squirrels. (Humans from Europe certainly gave it to armadillos in America—in that case, the chain of transmission has been established by the genetics.)"

While the hypothesis that the Viking squirrel trade spread leprosy might be an interesting one, current data remains inconclusive. Regardless, the study does indicate that there is still much to find out about leprosy today; even if the last human case in England was over 200 years ago. As Green notes, it is interesting to reflect on the fact that the last cases of leprosy in Europe were in fact within Scandinavia.

Sarah E. Bond is an Assistant Professor of Classics at the University of Iowa. For more on ancient and medieval history, follow her @SarahEBond.

I am an Assistant Professor in the Classics Department at the University of Iowa. I am interested in Roman, late antique, and early medieval history, archaeology, topography and GIS, Digital Humanities, and the role of Classics in pop culture (e.g., Game of Thrones). I obta...